Liquid crystal displays are commonly used as displays for compact electronic apparatuses, because they not only provide good quality images with little power but are also very thin. The liquid crystal in a liquid crystal display does not emit any light itself. The liquid crystal has to be lit by a light source so as to clearly and sharply display text and images. Thus, a backlight module is generally needed for a liquid crystal display.
Referring to FIG. 8, a typical backlight module 80 includes a light guide plate 82, a plastic frame 84, and a plurality of light emitting diodes (LEDs) 86. The light emitting diodes 86 are disposed adjacent to a light incident surface 822 of the light guide plate 80, and collectively serve as a light source. The plastic frame 84 defines a plurality of adjacent cutouts 842 at an inside of one main beam thereof. The light guide plate 82 is received in the plastic frame 84, and the light emitting diodes 86 are respectively received in the cutouts 842.
However, the sizes of the cutouts 842 may not accurately match the sizes of the light emitting diodes 86 due to imprecise manufacturing. When this happens, small gaps exist between the light emitting diodes 86 and the light incident surface 822 of the light guide plate 82 after the backlight module 80 has been assembled. These gaps may diminish the emitting luminance of the light guide plate 82.
FIG. 9 is a graph showing the negative impact of the above-mentioned gaps on the effective utilization of the emitting luminance. X represents the distance between the light emitting diodes 86 and the light incident surface 822 of the light guide plate 82 in millimeters (mm). Y represents the relative emitting luminance of the light guide plate 82 as a function of X. It can be seen that the greater the value of X, the lower the value of Y. That is, the greater the gaps, the lower the value of the relative emitting luminance.
What is needed, therefore, is a backlight module that can overcome the above-described deficiencies. What is also needed is a liquid crystal display employing such a backlight module.